This invention relates to a sample tab and sample housing for performing rapid spectrophotometric measurement of Hemoglobin A1c (HbA1c) in whole blood, without the use of any reagent.
Diabetes mellitus is due to absolute or relative insulin deficiency. The most common forms of diabetes are Type 1 or Insulin-dependent diabetes, and Type 2 or Non-insulin-dependent diabetes. What all forms of diabetes have in common is elevation in blood glucose or hyperglycemia. There are about 16 million diabetics in the US, with about 10-15% being Type 1 and the rest being Type 2. Type 1 diabetes is caused by an absolute insulin deficiency, and usually occurs before the age of 30, although it can occur at any age. Consequently, it was also referred to as juvenile diabetes. It is not associated with obesity and is commonly complicated by ketoacidosis. Ketoacidosis is an acute complication of diabetes, and may present as a medical emergency because of dehydration and acidosis (low blood pH). Type 2 diabetes usually develops after the age of 30 and is not associated with total loss of the ability to secrete insulin. Consequently, it was referred to as maturity-onset diabetes. Plasma insulin levels are often normal or elevated. Al most all the patients are obese, and their glucose tolerance may be restored to normal if they loose weight. They have a reduced number of insulin receptors, and the number of these receptors can increase with weight loss. Due to the presence of circulating insulin, ketoacidosis is a rare complication.
The late complications of all forms of diabetes are kidney failure (nephropathy), blindness (due to retinopathy), sensory deficits (due to neuropathy). Recent long-term clinical evaluations report that failure of a patient to maintain glucose levels as close to normal as possible can contribute to these significant complications of diabetes. To adequately control the glucose levels in their blood, diabetic patients must inject themselves with insulin once or twice daily, and must monitor their blood glucose levels between 1 and 4 times daily. The most common method used by diabetic patients for monitoring blood glucose, is to acquire a small sample of blood by sticking the finger with a lancet, and squeezing a droplet of blood onto a paper strip which is then placed on a detection device. The glucose results assist the patients in planing meals and physical activities, and also assist the doctors in optimizing the patients"" insulin dosage. Unfortunately, many diabetic patients are not compliant in measuring their blood glucose regularly, and regulating their diet and physical activities, but yet their glucose levels may be at acceptable levels during their visit to the doctor""s office. To get around this problem in detecting non-compliance, doctors monitor their patients"" HbA1c levels every 2 to 4 months.
HbA1c is one specific type of glycated Hb, constituting approx. 80% of all glycated Hb and is formed by the spontaneous reaction of glucose with the N-terminal amino group of the Hb A beta chain. The HbA1c and the glycated Hb values have a high degree of correlation, and either may be used in the management of diabetes. As a matter of fact, some in vitro diagnostic systems measure glycated Hb but report HbA1c results. Formation of HbA1c irreversible, and the blood level depends on both the life span of the red blood cells (average 120 days) and the blood glucose concentration. Therefore HbA1c represents the time-averaged blood glucose values over the preceding 4 to 6 weeks, and is not subject to the wide fluctuations observed in blood glucose values. Studies have shown that quality of life improves with decreasing levels of HBA1c, and measurements every 2 to 4 months are recommended.
The gold standard for measuring HbA1c uses high performance liquid chromatography (HPLC). Other methods use affinity chromatography, ion-exchange chromatography and immunoinhibition turbidimetric techniques. In all the available methods, the first step is the production of a hemolysate by lysing the red blood cells with a special reagent. Since no near-patient testing for HbA1c is currently available, diabetic patients have to visit their doctor a second time to discuss their HbA1c results. The inconvenience to patients and the extra cost for a follow-up visit to the doctor, prompted manufacturers to develop a kit, which enables the patient to place their blood on a specially-treated test strip, which is then sent to a laboratory in a prepaid mailer. Within 1 to 2 weeks, both patients and their doctors receive the HbA1c results. By mailing in a blood sample ahead of time, the follow-up visit to the doctor can be eliminated. A rapid method for performing the HbA1c test in the doctors office is still preferred.
It is desirable to provide an apparatus and a method whereby a doctor can test his/her patent""s HbA1c within minutes. It is preferred that the sample requirement is a drop of blood drawn by finger prick, in a manner comparable to near-patient glucose testing. The advantages of the present invention are the rapid turn-around time during a patient""s visit with his/her doctor, and the decreased costs due to absence of reagents.
In its broad aspect the present invention provides an apparatus for determining the concentration of HbA1c and Hb in a blood specimen where the apparatus comprises: a sample tab; a sample housing for receiving a sample; and a radiation source and radiation detector, operatively coupled with a means for providing a determination of glucose concentration in the blood sample based on the absorbed radiation.
According to one embodiment of the present invention, the sample housing comprises a block with a slit for inserting the sample tab, and more preferably, the sample tab consists of a slide or base plate with a depression or well in the base plate for containing the sample and a coverslip which closes when the tab is inserted in the housing, preferably, the cover closes automatically when inserted in the sample housing.
In a preferred embodiment of the present invention, the sample well contains two grooves and an overflow ring for collecting excess blood as it is squeezed out by the closing coverslip. Preferably, the coverslip is attached to the tab so that the blood proximate the coverslip hinge makes contact with the coverslip first; as the coverslip closes, excess blood is squeezed out through the two grooves and into the overflow ring.
Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.